[Leetcode] Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

Solution:

public class Solution {
    public boolean isValid(String s) {
        if (s == null || s.length() == 0)
            return true;
        if (s.length() == 1)
            return false;
        int N = s.length();
        int i = 0;
        Stack<Character> myStack = new Stack<Character>();
        while (i < N) {
            char temp = s.charAt(i);
            if (temp == '(' || temp == '{' || temp == '[') {
                myStack.push(temp);
                i++;
            } else {
                if (!myStack.isEmpty()) {
                    char t = myStack.pop();
                    if (((t == '(') && (temp == ')'))
                            || ((t == '{') && (temp == '}'))
                            || ((t == '[') && (temp == ']'))) {
                        i++;
                    } else {
                        return false;
                    }
                } else {
                        return false;
                }
            }
        }
        if(myStack.isEmpty())
            return true;
        else
            return false;
    }
}

我的代码风格太差了，贴一下大神的代码：

public class Solution {
    public boolean isValid(String s) {
        if (s == null)
            return false;
        Stack st = new Stack();
        for (int i = 0; i < s.length(); i++) {
            if(s.charAt(i)==']'||s.charAt(i)==')'||s.charAt(i)=='}'){
                if(st.empty())
                    return false;
                else{
                    char c= st.pop().toString().charAt(0);
                    if(!((c=='('&&s.charAt(i)==')')||(c=='['&&s.charAt(i)==']')||(c=='{'&&s.charAt(i)=='}'))){
                        return false;
                    }                
                }
            }else{
                st.push(s.charAt(i));
            }
        }
        return st.empty();
    }
}